1. Field of the Invention
This invention relates to a tape tension controlling apparatus for a reel shift deck mechanism and more particularly, to a tape tension apparatus, used for a magnetic recording and reproducing apparatus such as a video tape recorder (referred to hereinafter as a VTR), for controlling the tape tension at different positions according to various sizes of tape cassettes.
1. Description of the Conventional Art
A tape tension controlling apparatus used in a recent VTR is generally designed such that when a tape cassette is inserted in the cassette holder in a substantially horizontal state, the tape tension apparatus is operated at a predetermined position. In this case, the tape tension apparatus does not maintain a regular tension because a mounting position of a reel is fixed with respect to a base plate.
FIG. 1 illustrates a conventional tape tension controlling apparatus. In this mechanism, after a cassette is inserted, the tape T drawn from a reel 1 is guided through a pair of guide members 2 and 3.
A tension arm 4 is located at a predetermined position on a base plate (not shown). Also, the tension arm 4 pivots on a rotation shaft 5 provided at one end thereof and has a tension post 6 provided at the other end thereof. Thus, the tape T is driven around the tension post 6 between the guide members 2 and 3.
A tension band 7 is wound around a predetermined portion of a circumference of the reel 1. One end 8 of the tension band 7 is connected to the tension arm 4 and the other end 9 of the tension bend 7 is fixed on the base plate. Also, a tension spring 10 is connected at its one end to the tension arm 4 at a location opposed to the one end 8 of the tension band 7.
In order to maintain the tape tension, the tension arm 4 must be positioned at an equilibrium point of a tension band force Fb, a spring force Fs and a tension force F of the tape T. As a result, the tape tension controlling apparatus can only be controlled under certain conditions without applying an external force, and thereby the tape tension controlling apparatus cannot be widely utilized.
In this case, when the conventional tension controlling apparatus must be used with a one-fourth inch tape cassette, in case of changing the size of the tape cassette, the conventional tension controlling apparatus is not able to maintain a regular tension of the tape between the reel and the tension arm.